The European Space Agency (ESA) says its Philae probe drilled into its host comet November 14 but may lose power before it can transmit drilling data.
Charged with 60 hours of onboard power, Philae bounced twice after initial touchdown on November 12, settling in shadowed from sunlight that could have extended its battery life.
ESA official Stephan Ulamec said the drill "started" November 14 but contact between Philae and its orbiting mothership Rosetta was lost soon thereafter.
There are two communications windows per day.
It was not certain the drill had actually pierced the surface of comet 67P.
So far, the 100-kilogram lab has sent back the first-ever photos taken from a comet surface.
Scientists hope Philae will offer clues to the formation of the Solar System and the appearance of life on Earth.